Narimoto Ouka

Hobbies: Playing board games
Likes: The school her grandfather (the former principal) built, meat spaghetti
Dislikes: The adults who try to steal the school from her, carrots

Ouka is the Souto Gakuen's former principal's granddaughter. After he passed away, he entrusted the school to her, and she became its new principal despite just being a fourth grader in elementary school. Though she acts like her age, Ouka is also a formidable girl who is able to fiercely protect herself and the school.

Spoiler

At a certain moment before the arrest of Michinori, Haruta confesses his feelings to Ouka who accept them. While they are about to kiss, Ouka panics and tells to Haruta that it's illegal to start a relationship with a 9-year-old girl and asks him to wait until she is 18 years old.
In 2026 when she turn 18, she comes back to see Haruta except that... She still has her child's body (to her greatest regret having always wanted to have the same body as Miaya).